This invention relates to viscous couplings. More particularly, it relates to such couplings employed in automatic fluid coupling or torque converter transmissions to selectively bypass the torque converter.
Torque converter type automatic transmissions have achieved almost universal application and acceptance in motor vehicles. While generally satisfactory in this application, torque converter automatic transmissions embody inherent slip and therefore incorporate inherent losses in vehicular fuel economy. In an effort to minimize this slippage and thereby optimize fuel economy, various efforts have been made to bypass the torque converter with some manner of direct drive which is typically brought into play when the vehicle is operating in the higher gear ratios and above a predetermined vehicular speed. While these direct drive bypass arrangements have resulted in improvements in fuel economy, they have also, under certain conditions, served to transmit various drive line vibrations to the passenger compartment of the motor vehicle, resulting in a derogation in the ride quality of the vehicle. In an effort to provide a bypass arrangement that would not transmit drive line vibrations to the passenger compartment, it has been proposed that a viscous coupling be employed in the bypass drivetrain. While the use of a viscous coupling in the bypass drivetrain does serve to minimize transmission of drive line vibrations to the passenger compartment, it is imperative that the coupling be designed for maximum efficiency so that losses in the coupling itself cannot significantly offset the fuel economy gains achieved by the use of the bypass.
Further, since viscous couplings transmit torque across closely spaced internal surfaces via a viscous fluid, it is not only imperative that the spacing between the surfaces be uniform from one coupling to another but that such spacing be maintained while the coupling is in use. When viscous couplings are employed in bypass drivetrains, they are or may be subjected to relatively high axial loads which tend to distort their housings, thereby changing the spacing between the surfaces. Additionally, nonuniform axial loads on the housings tend to cock the housings and cause metal-to-metal contact of the internal surfaces, thereby causing dramatic derogation of the couplings performance and premature failure.
Viscous couplings employed in automatic torque converter transmissions to selectively bypass the torque converter must transmit relatively high torques and therefoe must have large viscous sheer surfaces, must be relatively compact to fit within the housing of the torque converter, must be manufacturable at reasonable and competitive cost, must exhibit uniform torque transmitting capacities from coupling-to-coupling, and must be durable. Accordingly, the viscous coupling disclosed herein is formed with an annular housing having an annular radially extending body member formed preferably as an aluminum casting, an annular radially extending cover member formed as a ferrous sheet metal stamping, a clutch member formed as a permanent mold casting disposed in a chamber defined by the housing. The body member includes an axially extending hub portion having an inner peripheral surface and the clutch member includes an axially extending hub portion having an outer peripheral surface on which the inner peripheral surface of the hub portion of the body member is journaled. The hub provides the sole radial and axial load support for the housing. And an outer peripheral portion of the steel cover member, fixed to an outer peripheral portion of the body member, defines an annular axially facing friction surface for clutching coaction with a confronting friction surface defined by the torque converter housing.